Well, I think you shouldn't give up on speech therapy. In my opinion the doctors wanted to encourage you to keep praticing. Beyond that, you should be aware that everyone's voices sound different than how they hear it themselves. Also, you can't just let the bullying make you sad. People make fun of you because they don't know how much their stupid bullshit hurts other people.

honestly I can say that the docs say you sound fine, because this is the best they can do at this point in medical time. the nasal sound will most likely always be there. so you sound fine to docs, because they think it wont get better. you are audible (which is still my favorite and most beautiful English word by the way).

i was priviledged that my gran taught me how to speak. i am not perfect but i have no nasal sound. my voice sounds like a sqeuk toy, so some people still make fun. but i don't mind because i am the first in my country to make history. my surgeon, which is considered to be the best of the best made me speak on a xray thing before my big ops. so he could see how i speak, because i have no nasal sound, which he couldn't figure out. in 1997 it was discovered that i do not use my vocal cords to speak. they sit there looking "pretty". i use my muscles for swallowing to speak. i was the first that ever did that. (first ever discovered, so it doesn't mean im the only one, just that im the first to get written down). no believed it was possible. but here i am.

so my advise is to get a "normal" that you trust more than anything and get them to sit behind you and speak. and you mimic them. record them and yourself. practice practice practice. it wont happen over night.

I still have speech problems and have an operation scheduled for this summer.
Don't give up on speech therapy, it can be really useful even if the progress is not that fast.
Most likely, your voice won't sound "normal" whatever that may be for you (I get what you mean, I'm actually having trouble with that too).
Actually my speech therapist said that the real goal is to be intellegible (by limiting nasal air interference-dont know how to name that one); there's not much we can do to change the tone of the voice itself.

Keep looking for a doctor who is committed to reducing nasality. There are many procedures, some old and some new that are very effective. I wouldn't rely on the opinion of a doctor. I would get the evaluation of an actual speech therapist who will give an honest opinion who can recommend more surgery and then pursue a surgeon who can help. Perhaps a speech therapist could recommend. Good luck!